Exhaust gas recirculation system

ABSTRACT

An exhaust gas recirculation system including pressure controlling means provided in the exhaust gas recirculation passage, said pressure controlling means having a pressure controlling section adapted to control air pressure in the pressure source with pressure of exhaust gas flowing into said pressure controlling means, and wherein pressure controlled by said pressure controlling section is led into a controlled pressure chamber defined by a diaphragm operable to open or close said pressure controlling means. A valve operated by pressure around a butterfly valve is provided in a conduit connecting said pressure source and said pressure controlling section. A chamber formed in said pressure controlling section for effecting pressure control is selectively communicated with said pressure source or with a part downstream of said butterfly valve. In the valve provided in the conduit connecting said pressure source and said pressure controlling section is provided a diaphragm chamber for operating said valve, the diaphragm chamber being communicated with a location adjacent said butterfly valve through a solenoid valve.

United States Patent 1 [111 3,881,456 Nohira et a1. 1 1 May 6, 1975EXHAUST GAS RECIRCULATION SYSTEM [75] Inventors: Hidetaka Nohira;Kiyoshi Kobashi, ABSTRACT both of Susono, Japan [73] Assignee: ToyotaJidosha Kogyo Kabushiki Kaisha, Toyota, Japan [22] Filed: May 29, 197421 1 Appl. No.: 474,351

Primary ExaminerWendell E. Burns Attorney, Agent, or Firm-Stevens,Davis, Miller & Mosher CONTROL DEVICE An exhaust gas recirculationsystem including pressure controlling means provided in the exhaust gasrecirculation passage, said pressure controlling means having a pressurecontrolling section adapted to control air pressure in the pressuresource with pressure of exhaust gas flowing into said pressurecontrolling means, and wherein pressure controlled by said pressurecontrolling section is led into a controlled pressure chamber defined bya diaphragm operable to open or close said pressure controlling means.

A valve operated by pressure around a butterfly valve is provided in aconduit connecting said pressure source and said pressure controllingsection.

A chamber formed in said pressure controlling section for effectingpressure control is selectively communicated with said pressure sourceor with a part downstream of said butterfly valve.

In the valve provided in the conduit connecting said pressure source andsaid pressure controlling section is provided a diaphragm chamber foroperating said valve, the diaphragm chamber being communicated with alocation adjacent said butterfly valve through a solenoid valve.

4 Claims, 4 Drawing Figures PATENTEUHAY' ems 3,881,456

sum 2 BF 2 FIG. 3

EXHAUST GAS RECIRCULATION SYSTEM BACKGROUND OF THE INVENTION 1. Field ofthe Invention:

This invention relates to an exhaust gas recirculation system forpurifying exhaust gas released from engines, and more particularly to asystem of the type just recited whereby exhaust gas recirculated isalways controlled by pressure to stay substantially at the same level asatmospheric pressure regardless of variation of negative pressure in theintake system of the engine and wherein particularly positive andreliable operation of the valve in the pressure control meanscontrolling the exhaust gas recirculation rate is ensured.

2. Description of the Prior Art:

In the conventional pressure control devices designed to control thesupply of exhaust gas into the intake system, recirculated exhaust gaspressure itself is introduced into a pressure chamber having a diaphragmso as to operate the valve in the pressure control unit by the action ofsaid diaphragm. Accordingly, pulsation of exhaust gas pressure isdirectly picked up, and hence in case only a small amount ofrecirculated exhaust gas is controlled, the valve and its seat hit orrub against each other to cause early wear thereof. It was thereforeessential to use a rubber-like material for the valve or for the valveseat, and for this reason, there is a certain limitation to heatresistance of such parts. Also, since pressure in the pressure chamberhaving the diaphragm is substantially equalized with atmosphericpressure, the valve itself is opened or closed with a weak force, sothat if such control valve is used, the exhaust gas flow characteristicof the control valve may be changed by the deposit material in exhaustgas, and further, as the valve is greatly affected by negative pressurein the intake pipe, it needs to additionally provide a certain negativepressure compensating means for improving responsiveness, but such meansitself involves the problem of heat resistance or sticking. There isalso known an automatic pressure controlling mechanism in which pressurein the pressure chamber having a diaphragm is detected by utilizingintake pipe negative pressure and air is introduced into the intake pipeto raise up the negative pressure in the intake pipe to a suitable levelto produce a controlling negative pressure signal so as to operate thevalve in the pressure controlling means in response to such signal tothereby maintain pressure in the pressure chamber substantially equal toatmospheric pressure. However, as this mechanism is of the type in whichair is flown into the intake pipe, there is a possibility that intakepipe negative pressure may be dropped below the lowest permissiblelevel. Therefore, intake pipe negative pressure is low at the high loadoperating range of the engine, and hence although it is desirable toenlarge the valve opening for allowing exhaust gas recirculation ingreat quantity at one time, it is actually impossible to obtain asatisfactorily large valve opening due to small intake pipe negativepressure. There is also proposed a device in which the valve is closedby the action of air pressure given by an engine-driven air pump, butaccording to this device, it is impossible to perfectly close thecontrol valve because the engine speed is low in the running conditionwhere perfect shut-off of exhaust gas recirculation is desired, asduring cranking or idling, and also because air pump pressure is weak.

SUMMARY OF THE INVENTION:

The present invention provides an improved exhaust gas recirculationsystem of the type in which the pressure of exhaust gas recirculatedfrom the exhaust system into the intake system is maintainedsubstantially equal to atmospheric pressure and the valve forcontrolling the exhaust gas recirculation rate can perform its openingand closing operations positively and reliably. According to the presentrecirculation system, a pressure control unit having a fixed throttle, apressure chamber and a valve are provided in the exhaust gasrecirculation conduit, and pressure in the controlled pressure chamberacting to open said valve is controlled by releasing compressed air froman air pump according to the pressure of the recirculated exhaust gas,thereby to maintain exhaust gas recirculated into the intake system atsubstantially the same level as atmospheric pressure, and further, whennegative pressure in the intake system indicating the running conditionof the engine drops below a certain level, supply of compressed air fromthe air pump into the controlled pressure chamber in the pressurecontrol unit is shut 011'. Also, positive pressure from the air pump andnegative pressure from the intake system are selectively supplied intothe controlled pressure chamber in the pressure control unit withoperation of a pressurechangeover valve in response to the enginerunning condition such that strong negative pressure working to theintake system will act when the valve is closed while high positivepressure of the air pump will act when the control valve is opened.Further, a solenoid-energized changeover valve is provided in a conduitthrough which negative pressure in the intake system is sent into thecontrolled pressure chamber, such that when there is no need ofrecirculating exhaust gas, as during warmup of the engine, thepressure-changeover valve maintains the shut-off condition of the airpump and the controlled pressure chamber in the pressure control unit bythe operation of said solenoid-energized changeover valve.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a schematic diagram of an exhaust gas recirculation systemaccording to the present invention;

FIG. 2 is a vertical sectional view of a pressure control unit in theexhaust gas recirculation system according to the present invention;

FIG. 3 is a vertical sectional view of a modification of pressurecontrol unit; and

FIG. 4 is a vertical sectional view of a pressurechangeover valve in theexhaust gas recirculation sys tem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

An exhaust gas recirculation system embodying the present invention isdescribed in detail with reference to FIG. 1. Air is supplied into theengine I from an air cleaner 2 while fuel-air mixture is suppliedthrough a Venturi 3, butterfly valve 4 and intake pipe 5, and theexhaust gas is discharged out from an exhaust pipe 6. Provided adjacentthe engine 1 is an air pump 8 which is driven by a crank shaft through abelt 7. The exhaust pipe 6 is connected to the intake pipe 5 through aconduit 10 provided with pressure controlling means 9 so that a part ofthe exhaust gas will flow into a section of the intake pipe 5 adjacentthe engine 1. Compressed air from the air pump 8 is conducted through aconduit 11 into a pressure inlet port 13 in a pressure-changeover valve12, and a pressure outlet port 14 of the valve 12 is connected through aconduit 17 to a pressure inlet port 16 in a pressure controlling sectionof a pressure control unit 9. The conduit 17 is also connected throughits branch conduit 17' to a pressure inlet port 19 of a controlledpressure chamber 18 in the pressure control unit 9. Another pressureinlet port 20 of the pressure-changeover valve 12 is connected through aconduit 22 to a negative pressure outlet port 21 which opens into asection of the intake pipe 5 located slightly downstream of the closedbutterfly valve 4. The negative pressure inlet port 24 of a negativepressure chamber 23 in the pressure-changeover valve 12 is connected toa negative pressure outlet port 25 opening into a section of the intakepipe 5 adjacent the closed position of the butterfly valve 4 through aconduit 27 which is provided with a solenoid-energized changeover valve26. This solenoid-energized changeover valve 26 is electrically operatedby a control device 28 which converts the engine speed into an electricsignal and produces an output signal corresponding to the engine speed.That is, the pressure-changeover valve 12 is arranged such that whenthere is no need of recirculating exhaust gas, the negative pressurechamber 23 in the changeover valve 12 is communicated with an opening 29(opened into the atmosphere) in the solenoid-energized changeover valve26, and when exhaust gas recirculation is required, the negativepressure chamber 23 is communicated with the negative pressure outletport 25 in the intake pipe 5. The input signal to the control device 28may be the warm-up condition of the engine or atmospheric temperature.

The pressure control unit 9 is now described in detail with particularreference to FIG. 2. There is provided a valve body 32 having an exhaustgas inlet 30, an L- shaped passage and an outlet 31. In the L-shapedpassage are provided a fixed throttle 33, a pressure chamber 34 and avalve 35 arranged in that order in the direction from the exhaust pipe 6to the intake pipe 5. The valve 35 consists of a valve seat 36 and avalve member 37, the latter being mounted slidably at the lowermost endof a shaft 38 so that the valve member 37 can seal the valve seat 36.The upper end of the shaft 38 extends through an air-bleeding hole 39upward of the valve body 32 and is secured to a diaphragm 40 by a nut.The air-bleeding hole 39 is adapted to prevent deposition of oilparticles to the shaft 38. In an atmosphere-communicated chamber 41below the diaphragm 40 is provided a spring 42 adapted to push up thediaphragm 40, and the controlled pressure chamber 18 is provided on theupper side of the diaphragm 40. In a side wall of the valve body 31 isprovided a detected pressure chamber 46 having a diaphragm 45, thechamber 46 being communicated with the pressure chamber 34 in thepressure control unit 9 through a passage 44 formed in the valve body 32and provided with a throttle 43. The passage 44 opens in a lower endportion of the detected pressure chamber 46 to flow down condensed waterinto the pressure chamber 34. Defined by the diaphragm 45 on theopposite side from the detected pressure cham ber 46 is a chamber 47which is communicated with the atmosphere through an air-bleeding hole48. On the chamber 47 side of the diaphragm 45 is provided a plate-likevalve 49 which has rubber-type synthetic resin layer on its surface andis fixed by a nut. In opposition to this valve 49 is provided anair-bleed pipe 52 which is connected to the pressure inlet port 16through a throttle and a check valve 51. The diaphragm 45 is arranged tobe moved by a spring 53 provided in the detected pressure chamber 46 anda spring 54 provided in the chamber 47 so as to maintain a small spacebetween the valve 49 and the air-bleed pipe 52 when no exhaust gaspressure works in the detected pressure chamber 46. The pressurecontrolling section 15 is constituted in this way. When pressure in thedetected pressure chamber 46 rises higher than the atmospheric pressure,the air-bleed pipe 52 is closed by the valve 49. The diaphragm 45 in thepressure control section 15 is disposed parallel to the direction oflateral vibration of the engine so that the diaphragm 45 may be isolatedfrom vibration of the engine.

FIG. 3 shows a modified form of pressure control unit 9. In thismodification, the parts assigned the same reference numerals as in theunit of FIG. 2 operate in the completely same way as the counterparts ofFIG. 2. The valve 35' is arranged such that the valve member 37' willengage with the valve seat 36' from its upper side, and two diaphragms57 and 58 are secured by a nut to the upper end of the shaft 38' in sucha manner that they are spaced apart a predetermined distance from eachother by a strut and a spring 56. The upper diaphragm 57 is greater inarea than the lower diaphragm 58, and a controlled pressure chamber 18having a pressure inlet port 19 is defined between said both diaphragms57 and 58. In a chamber 41' formed on the upper side of the diaphragm 57in communication with the atmosphere is provided a spring 59 adapted tourge the diaphragm 57 downwardly, said spring 59 being adjusted in itspushing force by an adjusting screw 60. Means corresponding to the checkvalve 51 in FIG. 2 is constituted by a check ball 62 hiased by a spring61 and a valve seat section 63 which are adapted to check introductionof atmospheric pressure into the side of the throttle 50. Beneath thediaphragm 58 is defined a chamber 64 communicated with the atmosphere.

The pressure-changeover valve 12 is shown in detail in FIG. 4. In thevalve body 65 is formed a chamber 66 connected to the pressure inletports 13, 20 and pressure outlet port 14, and a valve seat 67 isprovided between the pressure inlet port 13 and outlet port 14, with avalve seat 68 being provided between the pressure outlet port 14 andinlet port 20 in opposition to the valve seat 67. The valve seats 67 and68 are selectively closed by a valve 69 secured to the lower end of ashaft 70 which is secured at its top end to a diaphragm 72 by a nutthrough a seal 71 provided in the valve body 65 to seal the upper end ofthe chamber 66. Below the diaphragm 72 is defined a chamber 73communicated with the atmosphere, while a negative pressure chamber 23connected to the negative pressure inlet port 24 is formed on the upperside of the diaphragm 72. In the negative pressure chamber 23 isprovided a spring 74 adapted to push the diaphragm 72 downwardly, thespring 74 being adjusted in its pressing force by an adjusting screw 75.

Now, the operation of the exhaust gas recirculation system having theabove-described arrangement will be described. Let it here be assumedthat the control device 28 is issuing a signal requiring recirculationof exhaust gas in response to a factor such as engine speed oratmospheric temperature, and accordingly, the solenoid-energizedchangeover valve 26 is in operation to communicate the negative pressureoutlet 25 in the intake pipe 5 with the negative pressure inlet 24 inthe pressure-changeover valve 12. When no negative pressure is acting tothe negative pressure outlet port 25 in the intake pipe 5 as when theengine is cranking, idling, decelerated or heavily loaded, no negativepressure works to the negative pressure 23 in the pressurechangeovervalve 12, and hence the valve 69 keeps the valve seat 67 closed throughthe shaft 70 under the force of the spring 74. In this condition, sincethe pres sure-changeover valve 12 communicates the pressure inlet portwith the pressure outlet port 14, a high negative pressure is loaded tothe check valve 51 in the pressure controlling section 15 of thepressure control unit 9 from the negative pressure outlet port 21 in theintake pipe 5, thus keeping the check valve 51 closed, and hence anegative pressure acts to the controlled pressure chamber 18 from theconduit 17' irrespective of pressure in the detected pressure chamber46. Consequently, the valve seat 36 is closed by the valve member 37through the shaft 38 under the force of negative pressure acting to thediaphragm 40 and the force of spring 42, thus perfectly inhibiting flowof exhaust gas into the intake pipe 5 from the exhaust pipe 6 throughthe conduit 10.

When the engine is accelerated or brought into stationary run, with thesolenoid-energized changeover valve 26 being kept in the above-saidcondition, the negative pressure acting into the negative pressureoutlet port in the intake pipe 5 is now introduced into the negativepressure chamber 23 in the pressurechangeover valve 12 through conduit27 to move upwardly the valve 69 against the force of spring 74 tothereby close the valve seat 68. As this situation is brought about, thepressure-changeover valve 12 is operated to communicate the pressureinlet port 13 with the outlet port 14 so that compressed air from theair pump 8 is led to the pressure controlling section 15 in the pressurecontrol unit 9 through said pressurechangeover valve 12 and conduit 17.On the other hand, exhaust gas which has flown into the pressure chamber34 in the pressure control unit 9 is further introduced through thepassage 44 into the detected pressure chamber 46 to equalize pressure insaid pressure chamber 34 with that in said detected pressure chamber 46.Therefore, if pressure in the detected pressure chamber 46 is onlyslightly higher than atmospheric pressure, there is created a smallspace between the valve 49 mounted on the diaphragm 45 and the openingof the air-bleed pipe 52 by the force of springs 53 and 54, causingcompressed air in the conduit 17 to flow out into the chamber 47 throughthe throttle 50, check valve 51 and the air-bleed pipe 52 to raise thepressure of the exhaust gas in said conduit 17 close to atmosphericpressure. Accordingly, pressure in the controlled pressure chamber 18 inthe pressure control unit 9 also remains low and the diaphragm keeps thevalve 37 closed under the force of spring 42, inhibiting any flow ofexhaust gas through the valve 35 in the control unit 9. However. whenexhaust gas pressure in the pressure chamber 34 rises up to causecorresponding rise of pressure in the detected pressure chamber 46. thediaphragm is urged to move toward the chamber 47 to actuate the valve 49to close the air-bleed pipe 52. This causes pressure rise in theconduits l7 and 17' as well as pressure rise in the controlled pressurechamber 18, forcing the diaphragm 40 downwardly against the opposingforce of spring 42. Consequently, the valve member 37 separates from thevalve seat 36, allowing exhaust gas in the exhaust pipe 6 to flow intothe intake pipe 5 through conduit 10 and pressure control valve 9. Suchflow of exhaust gas into the intake pipe 5 causes a drop of pressure inthe pressure chamber 34 and in the detected pressure chamber 46,allowing compressed air to flow out into the chamber 47 from theair-bleeding pipe 52 to lower the pressure in the controlled pressurechamber 18 to thereby close the valve 35. Pressure in the pressurechamber 34 is thus maintained substantially equal to atmosphericpressure, and hence the amount of exhaust gas flowing to the outlet 31from the fixed throttle 33 is kept proportional to the amount of airintroduced into the engine I from the Venturi 3.

When the engine speed is such that no exhaust gas recirculation isrequired, or when the engine is not yet sufficiently warmed up, thecontrol device 28 operates to switch the solenoid-energized changeovervalve 26 to communicate the negative pressure chamber 23 in thepressure-changeover valve 12 with the atmosphere, and no matter how muchnegative pressure acts to the negative pressure outlet 25 of the intakepipe 5, the operation of the pressure changeover valve 12 is not theleast affected. This condition induces the same behavior as when theengine is cranking, idling, decelerated or heavily loaded, and the valve35 of the pressure control unit 9 is perfectly closed to inhibitrecirculation of exhaust gas in the exhaust pipe 6 into the intake pipe.

Now, the operation of the pressure control unit shown in FIG. 3 will bedescribed. This control unit operates substantially same as that of FIG.2, but in this unit, two diaphragms are provided above and below thecontrolled pressure chamber 18', and pressure in the chamber 18' foroperating the valve 35 acts to the differential area between the upperand lower diaphragms 57 and 58 to operate the valve member 37'. Thisvalve member 37 is positioned above the valve seat 36' to prevent thedeposition of carbon or the like in exhaust gas on the valve member 37'.

As described above, in the exhaust gas recirculation system of thepresent invention, pressure of compressed air supplied into the pressurecontrolling section from the air pump is controlled according topressure of the exhaust gas introduced into the pressure control unit,and the operation of the valve in the control unit is accomplished bythe controlled compressed air to maintain pressure of exhaust gasrecirculated into the intake system from the exhaust pipe at thesubstantially same level as atmospheric pressure. However, since thepressure acting to open the valve is a strong positive pressure, it ispossible to strengthen the acting force of the spring used formaintaining the valve in its closed position, and the exhaust gasrecirculated does not pulsate. Also, although compressed air introducedinto the pressure controlling section is released into the atmospherefrom the valve, there is posed no problem in operating the valve of thepressure control unit as air discharge from the air pump is great inamount. Further, said opening and closing operation of the valve islittle affected even if compressed air from the air pump is used forre-combustion of exhaust gas. Still further, the area where air pumpscharge pressure is weak,

that is, where the engine speed is low, coincides with the area where itis desired to shut off exhaust gas recirculation for securing safety ofthe engine. in such area, it is possible to perfectly shut off exhaustgas recirculation by converting the weak air pump discharge pressureinto a strong intake pipe negative pressure by use of apressure-changeover valve.

It is to be further noted that the pressure controlling section of thepressure control unit is secured directly to the valve body so that evenif the atmospheric temperature drops to an extremely low level, nofreezing of condensed water in the detected pressure chamber takes placeowing to radiation of heat from the control valve body. However, sincelittle exhaust gas flows into the detected pressure chamber, thepressure controlling section does not rise so high in temperature andhence long durability of the diaphragms is ensured. Also, since closureof the valve in the pressure control unit is accomplished by theresilient force of springs, it is not essential in some applications toutilize negative pressure in the intake system when closing the valve.

What we claim is:

I. An exhaust gas recirculation system in which the exhaust system andintake system of an internal combustion engine are connected to eachother by a conduit so as to recirculate a part of exhaust gas from theexhaust system into the intake system, said system comprising:

a pressure control unit provided in said conduit and having a fixedthrottle,

a pressure chamber and valve arranged successively in that order in thedirection from the exhaust system to the intake system,

a pressure control section comprising:

a first chamber communicated with said pressure chamber,

a second chamber separated from said first chamber by a diaphragm andcommunicated with a pressure source and also with the atmosphere, and

a valve assembly secured to said diaphragm and adapted to controlcommunication between said second chamber and said pressure source,

and a controlled pressure chamber communicated with said second chamberin said pressure control section and compartmented by a diaphragm joinedto said valve in said pressure control unit, whereby compressed airsupplied into said second chamber in said pressure control section fromsaid pressure source is released into the atmosphere corresponding topressure in said pressure chamber to control pressure in said chamber inthe pressure control section, and said valve in the pressure controlunit is operated responding to the thus controlled pressure so as tomaintain pressure in said pressure chamber substantially equal toatmosphere pressure.

2. The exhaust gas recirculation system as set forth in claim 1, whereina valve is provided in the conduit connecting the pressure source withsaid second chamber in the pressure control section and with saidcontrolled pressure chamber in the pressure control unit, and a negativepressure chamber operable to open or close said valve is connected tothat part of the intake system which is located adjacent a butterflyvalve so that said valve will be opened or closed according to therunning condition of the engine.

3. The exhaust gas recirculation system as set forth in claim 1, whereinsaid pressure source and a section of the intake system downstream ofthe butterfly valve are communicated with said second chamber in thepressure control section through a valve, and a negative pressurechamber operable to switch said valve is communicated with a part of theintake system adjacent said butterfly valve, and wherein said pressuresource and said intake system are selectively communicated with saidsecond chamber by said valve according to the running condition of theengine.

4. The exhaust gas recirculation system as set forth in claim 2, whereina solenoid-energized valve operated according to the running conditionof the engine is provided in the conduit connecting the negativepressure chamber in said valve with a part of the intake system adjacentthe butterfly valve, and when there is no need of recirculating exhaustgas, said negative pressure chamber in said valve and the intake systemare shut off from each other by said solenoid-energized valve.

1. An exhaust gas recirculation system in which the exhaust system and intake system of an internal combustion engine are connected to each other by a conduit so aS to recirculate a part of exhaust gas from the exhaust system into the intake system, said system comprising: a pressure control unit provided in said conduit and having a fixed throttle, a pressure chamber and valve arranged successively in that order in the direction from the exhaust system to the intake system, a pressure control section comprising: a first chamber communicated with said pressure chamber, a second chamber separated from said first chamber by a diaphragm and communicated with a pressure source and also with the atmosphere, and a valve assembly secured to said diaphragm and adapted to control communication between said second chamber and said pressure source, and a controlled pressure chamber communicated with said second chamber in said pressure control section and compartmented by a diaphragm joined to said valve in said pressure control unit, whereby compressed air supplied into said second chamber in said pressure control section from said pressure source is released into the atmosphere corresponding to pressure in said pressure chamber to control pressure in said chamber in the pressure control section, and said valve in the pressure control unit is operated responding to the thus controlled pressure so as to maintain pressure in said pressure chamber substantially equal to atmosphere pressure.
 2. The exhaust gas recirculation system as set forth in claim 1, wherein a valve is provided in the conduit connecting the pressure source with said second chamber in the pressure control section and with said controlled pressure chamber in the pressure control unit, and a negative pressure chamber operable to open or close said valve is connected to that part of the intake system which is located adjacent a butterfly valve so that said valve will be opened or closed according to the running condition of the engine.
 3. The exhaust gas recirculation system as set forth in claim 1, wherein said pressure source and a section of the intake system downstream of the butterfly valve are communicated with said second chamber in the pressure control section through a valve, and a negative pressure chamber operable to switch said valve is communicated with a part of the intake system adjacent said butterfly valve, and wherein said pressure source and said intake system are selectively communicated with said second chamber by said valve according to the running condition of the engine.
 4. The exhaust gas recirculation system as set forth in claim 2, wherein a solenoid-energized valve operated according to the running condition of the engine is provided in the conduit connecting the negative pressure chamber in said valve with a part of the intake system adjacent the butterfly valve, and when there is no need of recirculating exhaust gas, said negative pressure chamber in said valve and the intake system are shut off from each other by said solenoid-energized valve. 